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heme.hit.core.v1PRODUCTION
heme.hit.core.v1

Heparin-induced thrombocytopenia (HIT) — 4Ts + non-heparin anticoagulation

hematologyacuteadultgeriatric
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12/12 authored

Canonical 12-phase frame with authored status for this dossier.

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Detailed

Confirm clinical scenario: thrombocytopenia (platelet drop >50% from baseline OR drop to <150K) in patient on heparin exposure (any form, any duration); calculate 4Ts pretest probability (Thrombocytopenia / Timing / Thrombosis / oTher causes) — ASH 2018 PMID 30482768; Lo JTH 2006 PMID 16634744

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4Ts score calculated; low (≤3) effectively rules out HIT (high NPV); intermediate (4-5) or high (6-8) requires testing + empiric non-heparin AC — ASH 2018

Patient inputs (12)

Heparin exposure is sine qua non for HIT — UFH > LMWH risk; ANY form counts: prophylaxis, therapeutic, flushes, heparin-coated catheters, hemodialysis, ECMO, cardiac surgery — ASH 2018 PMID 30482768

Platelet drop >50% from baseline OR drop to <150K days 5-10 of heparin exposure is the diagnostic platelet trajectory; ≥50% drop scores highest in 4Ts — Lo JTH 2006 PMID 16634744

Days since heparin started drives 4Ts timing score: typical onset days 5-10; rapid-onset <24 h if recent exposure within 100 d; delayed-onset after heparin discontinued (rare) — ASH 2018

New arterial / venous thrombosis on heparin is HIGH 4Ts (HITT); limb ischemia drives emergent intervention — ASH 2018

oTher causes scoring in 4Ts: sepsis, drugs (vanco, linezolid, fluoroquinolones), DIC, post-transfusion purpura, ITP exacerbation, marrow suppression — ASH 2018

Baseline platelet count before heparin is essential for percent-drop calculation — ASH 2018

CrCl drives non-heparin AC selection: argatroban (hepatic clearance) preferred in renal failure; bivalirudin needs dose reduction in CrCl <30; fondaparinux contraindicated if CrCl <30 — ASH 2018

Hepatic function drives non-heparin AC selection: argatroban requires dose reduction in significant hepatic dysfunction (Child-Pugh B/C — start at 0.5 mcg/kg/min); bivalirudin preferred in hepatic dysfunction — ASH 2018

Coagulation panel to rule out DIC (high fibrin degradation products, low fibrinogen, prolonged PT/aPTT) which overlaps HIT and may co-exist (autoimmune HIT with DIC; severe HIT — Greinacher JTH 2017 PMID 28846826)

SRA is the functional confirmatory test; high specificity (>95%) but limited availability and slow turnaround — start non-heparin AC empirically while awaiting SRA — ASH 2018

Future heparin re-exposure planning: HIT antibodies clear over ~100 days; cardiac surgery during seropositive period requires bivalirudin (or wait if non-urgent) — ASH 2018

PF4/heparin antibody ELISA: sensitive (98%+) but only modestly specific (~50%); positive supports HIT but does NOT confirm (cross-reactivity, asymptomatic seroconversion); negative effectively rules out HIT in intermediate-high pretest — ASH 2018

* = hard-required. Engine cannot meaningfully run until these are filled.

Severity triggers (5)

5 need judgement
  • informationallife_threateninghitt_with_major_thrombosis
    HIT with new major thrombosis (DVT/PE/MI/stroke/limb ischemia/mesenteric ischemia) on heparin — ASH 2018
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateninglimb_threatening_hitt_ischemia
    Limb-threatening arterial or venous gangrene from HIT/HITT — ASH 2018; CHEST 2021
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningvenous_limb_gangrene_from_warfarin_in_acute_hit
    Venous limb gangrene or warfarin-induced skin necrosis from premature warfarin during acute HIT thrombocytopenia — ASH 2018
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateninganaphylactoid_reaction_post_iv_heparin_bolus
    Acute anaphylactoid reaction (rigors, hypotension, dyspnea, cardiac arrest) within minutes of IV heparin bolus in previously-sensitized patient — ASH 2018
    Trigger could not be auto-evaluated — needs clinician judgement.
  • informationallife_threateningautoimmune_hit_with_dic
    Autoimmune HIT spectrum: spontaneous HIT, persisting HIT, severe HIT with concomitant DIC — Greinacher JTH 2017 PMID 28846826
    Trigger could not be auto-evaluated — needs clinician judgement.

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Recommended regimen

Non-heparin anticoagulation for acute HIT (intermediate/high 4Ts) — ASH 2018 PMID 30482768
axis: non_heparin_anticoagulation_acute_hitstep 1 - Argatroban — first-line direct thrombin inhibitor; preferred in renal failure — ARG-911 Lewis Circulation 2001 PMID 11294800
Selected step "Argatroban — first-line direct thrombin inhibitor; preferred in renal failure — ARG-911 Lewis Circulation 2001 PMID 11294800" — Acute HIT (intermediate/high 4Ts) in patients with normal-to-mild hepatic function; renal failure does not require dose adjustment (hepatic clearance)
  • argatroban
    first line
    direct_thrombin_inhibitor
    2 mcg/kg/min IV continuous (reduce to 0.5 mcg/kg/min if significant hepatic dysfunction Child-Pugh B/C); titrate to aPTT 1.5-3x baseline (or anti-IIa target) • IV • continuous infusion (max: 10 mcg/kg/min in patients without hepatic dysfunction; titrate by aPTT 1.5-3x)
    triggers: acute_hit_intermediate_or_high_4ts, normal_or_mild_hepatic_function, renal_failure_friendly
    ARG-911 (Lewis Circulation 2001 PMID 11294800) — argatroban significantly reduced composite of death, amputation, new thrombosis vs historical controls in HIT and HITT. Hepatic clearance allows safe use in renal failure; dose-reduce to 0.5 mcg/kg/min if Child-Pugh B/C.
    rxcui 15202

inpatient playbook — drug actions (3)

  1. 1. argatroban
    rxcui 15202
    2 mcg/kg/min IV (0.5 mcg/kg/min if hepatic dysfunction) • IV • continuous infusion
    trigger: Intermediate/high 4Ts — start empirically before SRA result — ARG-911 PMID 11294800
    First-line non-heparin AC for HIT; hepatic clearance friendly to renal failure; titrate by aPTT 1.5-3x
  2. 2. bivalirudin
    rxcui 60819
    0.15 mg/kg/h IV • IV • continuous infusion
    trigger: Significant hepatic dysfunction or cardiac surgery anticoagulation — ASH 2018
    Preferred over argatroban in Child-Pugh B/C; short half-life favors peri-procedural use
  3. 3. fondaparinux
    rxcui 321208
    5-10 mg SC daily by weight (CrCl ≥30) • SC • daily
    trigger: Stable HIT, no major thrombosis progression, CrCl ≥30 — ASH 2018
    Pentasaccharide; theoretical non-cross-reactivity; simpler dosing; OFF-LABEL but supported by ASH 2018

Auto-drafted A&P note

inpatient

Subjective

- Possible entry pathways: Platelet drop >50% (or to <150K) days 5-10 of heparin exposure — calculate 4Ts (ASH 2018 PMID 30482768); New arterial or venous thrombosis on heparin (DVT/PE/limb ischemia/CVA/MI) — high 4Ts probability (ASH 2018 PMID 30482768); Skin necrosis at heparin SC injection site — pathognomonic for HIT regardless of platelet count (ASH 2018).

Objective

- No vitals, labs, or imaging entered for this encounter.

Assessment

**Heparin-induced thrombocytopenia (HIT) — 4Ts + non-heparin anticoagulation** (heme.hit.core.v1).
Phenotype framing: Distinguish HIT from competing thrombocytopenia causes: sepsis-induced thrombocytopenia (often DIC features; explains 4Ts oTher), drug-induced thrombocytopenia (vancomycin / linezolid / fluoroquinolones / GP2b3a inhibitors — abrupt drop on drug initiation), post-transfusion purpura (recent transfusion within 7-14 d, severe thrombocytopenia <20K, anti-HPA-1a antibodies), ITP exacerbation, pseudothrombocytopenia (EDTA platelet clumping — repeat in citrate tube), marrow suppression, DIC (low fibrinogen, schistocytes, high D-dimer — but may coexist with autoimmune HIT) — ASH 2018; Greinacher JTH 2017
Scope: Confirm clinical scenario: thrombocytopenia (platelet drop >50% from baseline OR drop to <150K) in patient on heparin exposure (any form, any duration); calculate 4Ts pretest probability (Thrombocytopenia / Timing / Thrombosis / oTher causes) — ASH 2018 PMID 30482768; Lo JTH 2006 PMID 16634744

No severity triggers fired against current inputs.

Plan

Regimen axis: **Non-heparin anticoagulation for acute HIT (intermediate/high 4Ts) — ASH 2018 PMID 30482768** — step "Argatroban — first-line direct thrombin inhibitor; preferred in renal failure — ARG-911 Lewis Circulation 2001 PMID 11294800".
1. argatroban 2 mcg/kg/min IV continuous (reduce to 0.5 mcg/kg/min if significant hepatic dysfunction Child-Pugh B/C); titrate to aPTT 1.5-3x baseline (or anti-IIa target) IV continuous infusion (direct_thrombin_inhibitor, first line) — ARG-911 (Lewis Circulation 2001 PMID 11294800) — argatroban significantly reduced composite of death, amputation, new thrombosis vs historical controls in HIT and HITT. Hepatic clearance allows safe use in renal failure; dose-reduce to 0.5 mcg/kg/min if Child-Pugh B/C.

Setting playbook (inpatient) — Diagnose HIT (4Ts + PF4 ELISA + SRA); STOP all heparin; start non-heparin anticoagulation; manage HITT thrombosis; monitor platelet recovery; plan transition to long-term AC — ASH 2018 PMID 30482768
2. argatroban 2 mcg/kg/min IV (0.5 mcg/kg/min if hepatic dysfunction) IV continuous infusion — Intermediate/high 4Ts — start empirically before SRA result — ARG-911 PMID 11294800 (First-line non-heparin AC for HIT; hepatic clearance friendly to renal failure; titrate by aPTT 1.5-3x)
3. bivalirudin 0.15 mg/kg/h IV IV continuous infusion — Significant hepatic dysfunction or cardiac surgery anticoagulation — ASH 2018 (Preferred over argatroban in Child-Pugh B/C; short half-life favors peri-procedural use)
4. fondaparinux 5-10 mg SC daily by weight (CrCl ≥30) SC daily — Stable HIT, no major thrombosis progression, CrCl ≥30 — ASH 2018 (Pentasaccharide; theoretical non-cross-reactivity; simpler dosing; OFF-LABEL but supported by ASH 2018)

Non-pharmacologic actions:
- STOP all heparin: IV infusion, SC LMWH, all flushes (use citrate for lines), heparin-coated catheters, hemodialysis (citrate or argatroban) — ASH 2018
- Heparin allergy / contraindication label in EMR + bedside — ASH 2018
- Medical alert ID + patient education — ASH 2018
- AVOID prophylactic platelet transfusion — ASH 2018 strong recommendation; transfuse only for active bleeding
- Hematology consult — ASH 2018
- Lower-extremity Doppler ultrasound for limb symptoms — ASH 2018
- CTPA if dyspnea / chest pain — ASH 2018
- Catheter-directed thrombolysis or thrombectomy for limb-threatening HITT — CHEST 2021

AVOID / contraindication checks:
- STOP_ALL_heparin_immediately_upon_intermediate_high_4Ts_including_flushes_LMWH_heparin_coated_catheters — ASH 2018 strong recommendation
- NEVER_warfarin_alone_during_acute_thrombocytopenia_protein_C_deficiency_venous_limb_gangrene_skin_necrosis — ASH 2018 strong recommendation
- AVOID_prophylactic_platelet_transfusion_may_worsen_thrombosis — ASH 2018 strong recommendation; transfuse only for active bleeding
- Argatroban_dose_reduce_0_5_mcg_kg_min_if_Child_Pugh_B_C — ARG 911 Lewis Circulation 2001
- Fondaparinux_CI_if_CrCl_lt_30_no_reversal — ASH 2018
- Bivalirudin_dose_reduce_if_CrCl_lt_30 — ASH 2018

Monitoring

Regimen monitoring:
- aPTT q4 6h during argatroban or bivalirudin titration — ASH 2018
- daily platelet count until recovery to gt 150K — ASH 2018
- LFT q1 3d on argatroban hepatic clearance — ASH 2018
- creatinine daily on bivalirudin — ASH 2018
- clinical thrombosis surveillance daily — ASH 2018

Setting (inpatient) monitoring:
- Daily platelet count until recovery >150K — ASH 2018
- aPTT q4-6h during argatroban/bivalirudin titration — ASH 2018
- LFT q1-3 d on argatroban — ASH 2018
- Anti-Xa for fondaparinux titration if used therapeutic — ASH 2018
- Clinical thrombosis surveillance daily — ASH 2018

Follow-up plan: Duration: isolated HIT (no thrombosis) → minimum 4 weeks of anticoagulation (until platelet recovery + several days stable platelets); HITT (HIT with thrombosis) → at least 3 months — ASH 2018. Long-term: lifelong heparin avoidance documented in chart and medical-alert ID; HIT antibodies decline over ~100 days; if heparin re-exposure required emergently (cardiac surgery) AND antibodies still positive → use bivalirudin intraop; if antibodies negative ≥100 d post-event → heparin may be used short-course (cardiac surgery, hemodialysis) with close monitoring. Hematology follow-up at 1 mo, 3 mo, and 1 year; consider switch from warfarin to DOAC once HIT resolved and patient stable — ASH 2018
- Close-out criterion: Duration plan documented (≥4 wk isolated HIT, ≥3 mo HITT); lifelong heparin avoidance counseled; re-exposure planning if relevant — ASH 2018

Monitoring phase: Daily platelet count until recovery >150K; aPTT or anti-IIa for argatroban / bivalirudin titration; anti-Xa for fondaparinux titration; daily clinical surveillance for new thrombosis (limb pain/swelling, chest pain/dyspnea, neuro changes, abdominal pain); LFT q1-3 d on argatroban; renal function on bivalirudin; coagulation profile q1-2 d initially — ASH 2018

Disposition

Current setting: inpatient — Diagnose HIT (4Ts + PF4 ELISA + SRA); STOP all heparin; start non-heparin anticoagulation; manage HITT thrombosis; monitor platelet recovery; plan transition to long-term AC — ASH 2018 PMID 30482768

Disposition criteria:
- Discharge when: platelets >150K stable, non-heparin AC therapeutic, no active thrombosis progression, transition AC plan documented (DOAC or warfarin), follow-up arranged — ASH 2018
- ICU transfer for: HITT with hemodynamic compromise, anaphylactoid reaction, limb-threatening ischemia — ASH 2018

Escalation triggers (move to higher acuity):
- New thrombosis on non-heparin AC → reassess AC dose, consider catheter-directed thrombolysis — ASH 2018
- Limb-threatening ischemia → emergent vascular surgery or IR consult — CHEST 2021
- Anaphylactoid reaction after IV heparin bolus → ICU, fluid + pressor support, non-heparin AC — ASH 2018
- Premature warfarin → vitamin K rescue + non-heparin AC continuation — ASH 2018

Earlier-Return Triggers

Return-precaution thresholds (watch for):
- [LIFE_THREATENING] HIT with new major thrombosis (DVT/PE/MI/stroke/limb ischemia/mesenteric ischemia) on heparin — ASH 2018
- [LIFE_THREATENING] Limb-threatening arterial or venous gangrene from HIT/HITT — ASH 2018; CHEST 2021
- [LIFE_THREATENING] Venous limb gangrene or warfarin-induced skin necrosis from premature warfarin during acute HIT thrombocytopenia — ASH 2018

Citations

- ASH 2018 HIT guidelines (Cuker Blood Adv 2018) + 4Ts validation (Lo JTH 2006) + ARG-911 (Lewis Circulation 2001) + autoimmune HIT review (Greinacher JTH 2017) [PMID:30482768](https://pubmed.ncbi.nlm.nih.gov/30482768/)
- Cited evidence (PMID 16634744) [PMID:16634744](https://pubmed.ncbi.nlm.nih.gov/16634744/)
- Cited evidence (PMID 11294800) [PMID:11294800](https://pubmed.ncbi.nlm.nih.gov/11294800/)
- Cited evidence (PMID 28846826) [PMID:28846826](https://pubmed.ncbi.nlm.nih.gov/28846826/)
- Cited evidence (PMID 28725494) [PMID:28725494](https://pubmed.ncbi.nlm.nih.gov/28725494/)

Last reconciled with current guidelines: 2026-05-26.
References
  • ASH 2018 HIT guidelines (Cuker Blood Adv 2018) + 4Ts validation (Lo JTH 2006) + ARG-911 (Lewis Circulation 2001) + autoimmune HIT review (Greinacher JTH 2017) — PMID:30482768
  • Cited evidence (PMID 16634744) — PMID:16634744
  • Cited evidence (PMID 11294800) — PMID:11294800
  • Cited evidence (PMID 28846826) — PMID:28846826
  • Cited evidence (PMID 28725494) — PMID:28725494